| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 104 === South China Sea (SCS) is the largest marginal sea located to the southeast of the Eurasian continent. The west, north and south portions of the South China Sea belong to continental shelves, while the Manila subduction zone exists in the east of the South China. The onset of seafloor spreading in the South China Sea was suggested to be ～32 Ma. After a ridge jump around 25 Ma, the Southwest sub-basin started to open. The spreading of the entire basin ended at ~16 Ma, then a phase of post-magmatic seamount formation has occurred.
As shown in the magnetic stripes of the ocean floor, the age of the oceanic crust increases with the distance away from the mid-ocean ridges. The thermal structures of the oceanic curst away from mid ocean ridge are different because of the plate cooling. Previous studies suggested that the oceanic crust depth is proportional to the square root of the mean age. In this study, we use 22 reflection seismic profiles distributed in the South China Sea and the associated magnetic age. After sediment correction, we suggest that the oceanic crust depth in the South China Sea is also directly proportional to the square root of the mean age of the South China Sea. The subsidence rate in the South China Sea is slower and the initial depth of the ridge is deeper than other oceans. However, the mantle lithosphere thickness beneath ridge in South China Sea is thinner than other ocean basins. We suggest that it would be due to a hotter mantle beneath the South China Sea.
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